plankton

If you set your pet goldfish free in a lake, he might dine on plankton instead of the food you sprinkle in his tank every day. Or, more likely, he might be dinner for a bigger fish.

Lakes, seas, and oceans are full of plankton, most of which is so small it can't be seen without a microscope. Anything that floats near the surface is considered to be plankton, whether it's an animal, plant, or something smaller like bacteria, and it's one source of food for fish and whales. The Greek root, planktos, means "wandering or drifting."

Definitions of plankton
1

n the aggregate of small plant and animal organisms that float or drift in great numbers in fresh or salt water

Type of:
being, organism
a living thing that has (or can develop) the ability to act or function independently

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